Polyurethane-polysulfonic acid esters which have a linear structure are known. They may be prepared, for example, by adding a sulfonic acid ester diol to the reaction mixture used for synthesizing a polyurethane. In German Pat. Nos. 1,156,977 and 1,184,946 it is proposed to react polyether-diols with diisocyanates and glycerol-monotosylate to produce polyurethane-polysulfonic acid esters which are then used for a quaternization reaction with mono-functional or di-functional tertiary amines to produce polyurethane-ionomers. In these products, side-chain aromatic sulfonic acid ester units are attached to an aliphatic chain segment. In the quaternization reaction, the aromatic sulfonic acid group is split off as an anion.
From U.S. Pat. No. 3,826,769, it is known to prepare polyurethanes on the basis of polyisocyanate-sulfonic acids, both polyurethane-polysulfonic acids and salts thereof being obtained. These polyurethanes are prepared either by sulfonating monomeric diisocyanates, such as tolylene diisocyanate, with sulfur trioxide and then using the resulting sulfonated diisocyanate as part of the isocyanate component for synthesizing a polyurethane or by first preparing a prepolymer having isocyanate end groups in the conventional manner and then sulfonating this with sulfuric acid by a reaction which is accompanied by partial chain-lengthening. The reaction products which contain sulfonic acid groups are then neutralized with a base and mixed with water, whereby aqueous polyurethane-ionomer dispersions are obtained. Polyurethanes which are modified with sulfonic acid groups or sulfonate groups in this way are frequently highly hydrophilic. For this reason, the sulfonic acid group content is generally kept as low as possible. When preparing dispersions, for example, one would only introduce the minimum quantity of sulfonate groups necessary to disperse the polyurethanes adequately and produce a stable dispersion. A higher sulfonic acid group content would impair the water-resistance of coatings obtained from the dispersions. For this reason, it is recommended to use only from 0.1 to 2% of sulfonating agent, based on the quantity of polyurethane, for preparing dispersions.
The preparation of polyurethanes and polyureas having a high filler content using polyisocyanate-sulfonic acids has also been disclosed in German Offenlegungsschrift No. 2,359,611. In this case, the sulfonic acid groups give rise to particular interactions between the organic binder and the fillers used, whereby high bonding forces are produced even when only very small quantities of binder are used. Where inorganic fillers are used, neutralization of the sulfonic acid groups generally takes place directly on the surface of the particles. In this process, again, only a proportion of the polyisocyanates used are sulfonated in order not to adversely affect the water-resistance and moisture-resistance of the composite materials obtained.
The exclusive use of polyisocyanates in the form of the sulfonic acids thereof would be of particular interest both from a technical point of view and from the point of view of toxicology and industrial hygiene. The sulfonic acids of aromatic isocyanates are pulverulent substances which have no vapor pressure and are therefore very safe to work with. Moreover, degradation of these isocyanates and of the polyaddition products produced from them gives rise to water-soluble diamino sulfonic acids which appear to be non-toxic. However, when isocyanatosulfonic acids are used alone for the synthesis of polyaddition products, the products obtained are highly hydrophilic and in many cases even water-soluble.
There is therefore a demand for a process which enables isocyanatosulfonic acids to be used as the sole isocyanate component and at the same time enables hydrophobic, water-resistant polyurethanes to be obtained. A solution to this problem is an object of the present invention.